Many different housings have been created to retain electrical terminals. In U.S. Pat. No. 2,469,397 multiple connectors are stacked in a housing. The stacked connectors are held together by clamping or strap means. In U.S. Pat. No. 2,928,066 housing blocks containing electrical terminals are interlocked using cylindric tongues and cylindric recesses. U.S. Pat. No. 3,253,252 describes sectional terminal blocks. Each connector has a key along one side of its housing and a corresponding slot on the opposite side. No modular units are employed. U.S. Pat. No. 3,259,870 describes individual connector units having dovetail tongues and correspondingly shaped grooves on opposite sides that allow interlocking connectors.
The following additional U.S. Pat. Nos. also show various systems of joining electrical connectors: 3,456,231; 3,676,833; 3,701,087; 3,789,343; 3,884,544. All of these interlocking connectors are limited in their versatility. What is needed is an easily separable and joinable series of connector units that provide an infinite number of possible combinations of connector blocks enclosing electrical terminals.